Knowledge of the accuracies of air bearing spindles in the sub-micrometre to nanometre range is required for the design, commissioning and operation of ultra-precise machine tools, measurement systems and other machines employing high precision rotational motion. In order to verify the dynamic performance of a spindle, measurement is required of its error motions in the unwanted five degrees of freedom (one axial, two tilts and two radial motions). Presentation of these error motions (eg in the form of polar charts) can then be used to provide critical spindle metrology data including total, asynchronous and average error motion rosette profiles and their average and peak values. This thesis describes a metrology system based on optical interferometry for measuring such unwanted error motions in three degrees of freedom involving motion along the spindle axis (axial rectilinear displacement and tilts about orthogonal axes), incurred with rotation of a precision air spindle over its specified speed-range. The system is not sensitive to orthoaxial translations which may be measured using alternative methods. Possible alternative techniques for measuring any of the degrees of freedom include an array of proximity sensors, (one for each translational degree of freedom and a further one for each of the other rotational degrees of freedom), to measure the run-out of an artefact. Proximity sensors based upon capacitive or optical fibre back-scatter techniques each offer the required single degree-of-freedom non-contacting capability and bandwidth. In the current work, a Fizeau interferometer is used to monitor the motion of the spindle of a vertical axis ultra-precision facing machine using a test-artefact. This is a mirror with less than one fringe departure from planarity from which interferogram. fringe-patterns are captured, digitised and analysed synchronously as the spindle rotates. The issue of the prediction of the dynamic form and motions of the observed interferograrn arises and the earlier theory is extended to optimise the set-up, including provision of automatic servo- alignment of the optical axis with the axis of the spindle. Measurement interferograrn data is sampled at selected angular incremental positions of spindle-rotation and image processing techniques used to filter the fringe pattern, enabling measurement of spindle tilt and axial displacement. Issues of sampling with respect to the anticipated spatial angular frequency of the spindle run-out are considered with respect to the speed/frequency capability of data-acquisition and processing arrangements. Essentially, with a spindle rotating at typical machining speeds of 300- 3000 rev/min, for consistent error motions, the resolution of an error plot is principally a function of observational time. It is foreseen that the system will be applicable in research and production-support in ultra-precision machining production processes and in rotational metrology.

No description available.

Among the various challenges involved in the development of CubeSats lies the attitude determination and control of the satellite. The importance of a properly functioning attitude determination and control system (ADCS) on any satellite is vital to the satisfaction of its mission objectives. Due to this importance, three-axis attitude control simulators are commonly used to test and validate spacecraft attitude control systems before flight. However, these systems are generally too large to successfully test the attitude control systems on-board CubeSat-class satellites. Due to their low cost and rapid development time, CubeSats have become an increasingly popular platform used in the study of space science and engineering research. As an increasing number of universities and industries take part in this new approach to small-satellite development, the demand to properly test, verify, and validate their attitude control systems will continue to increase. An approach to CubeSat attitude determination and control simulation is in development at the Virginia Tech Space Systems Simulation Laboratory. The final test setup will consist of an air bearing platform placed inside a square Helmholtz cage. The Helmholtz cage will provide an adjustable magnetic field to simulate that of a low earth orbit (LEO), and the spherical air bearing will simulate the frictionless environment of space. In conjunction, the two simulators will provide an inexpensive and adjustable system for testing any current, and future, CubeSat ADCS prior to flight. Using commercial off the shelf (COTS) components, the Virginia Tech CubeSat Attitude Control Simulator (CSACS), which is a low cost, lightweight air bearing testing platform, will be coupled with a 1.5-m-long square Helmholtz cage design in order to provide a simulated LEO environment for CubeSat ADCS validation. / Master of Science / The attitude determination and control subsystem is a vital component of a spacecraft. This subsystem provides the pointing accuracy and stabilization which allows a spacecraft to successfully perform its mission objectives. The cost and size of spacecraft are dependent on their specific applications; where some may fit in the palm of your hand, others may be the size of a school bus. However, no matter the size, all spacecraft contain some form of onboard attitude determination and control. This leads us to the introduction of a miniaturized class of spacecraft known as CubeSats. Their modular 10×10×10 cm cube structural design allows for both low cost and rapid development time, making CubeSats widely used for space science and engineering research in university settings. While CubeSats provide a low cost alternative to perform local, real-time measurements in orbit, it is still very important to validate the attitude determination and control subsystem before flight to minimize any risk of failure in orbit. Thus, the contents of this thesis will focus on the development, design, and testing of two separate spacecraft attitude determination and control simulation systems used to create an on-orbit environment in a laboratory setting in order to properly validate university-built CubeSats prior to flight.

The recently-developed simultaneous solution scheme for solving nonlinear rotordynamic systems running on foil-air bearings (FABs) has overcome the practice of decoupling the air film, foil and rotor equations that has been typically followed to reduce computational burden at the expense of accuracy. However, the published works using the simultaneous solution technique have been limited to a simple bump foil model in which the individual bumps were modelled as independent spring-damper (ISD) subsystems. The overall aim of this thesis is to present methods that enable more realistic FAB models to be integrated into the simultaneous solution scheme, without compromising its efficiency. Two such alternative approaches are presented: (1) the full foil structure modal model (FFSMM) of the bump foil structure; (2) non-parametric system identification of the entire FAB i.e. foil and air film. The FFSMM provides a more realistic model of the bump foil structure since it considers the interaction between the bumps and foil inertia. Although the foil damping is still assumed to be linear, the model presented is adaptable to nonlinear friction forces. The dynamics of the bump foil structure are studied by finite element methods and experimentally validated using a purpose-made corrugated foil structure. The FE result shows that the effect of bump interaction increases the effective stiffness of the FAB. Foil inertia is not important for the range of speeds considered in the thesis, but the experimentally validated fundamental foil resonance of around 2 kHz is within the operating speed range of high-speed turbomachinery. The FFSMM can take into account the curvature of the bearing sleeve, but the effect of this feature is proven to be negligible for the size of bearing used in the study. The FFSMM simulation results are correlated against ISD model results and published experimental maximum film thickness and locus of the journal response. The results of the FFSMM were then compared against experimental results under unbalance response conditions measured from a purpose-built test rig. The rotor was mathematically modelled using rigid body equations of motion, which were validated by modal analysis. The unbalance rotor response results obtained from the FFSMM and experiment both show that the sub-synchronous motion is not only mainly influenced by the increment of unbalance mass, but, to a greater extent, the increment of rotor speed. The findings show good agreement between the model and experimental results. This thesis also presents the non-parametric system identification of a FAB, which is also adaptable to the simultaneous solution scheme. This work is motivated by two advantages: (a) it removes computational limitations by replacing the whole bearing equations by a displacement/force relationship, where the air film effect is taken into account; (b) it can capture complications that cannot be easily modelled, if the identification is based on empirical data. A Recurrent Neural Network (RNN) is trained to identify the full numerical model of a FAB over a wide range of speeds. The identified model of the FAB is adapted into the frequency domain rotor-dynamic simultaneous solution technique by using harmonic balance (HB) methods, thus directly producing the steady-state orbit response. Excellent correlation is demonstrated between the identification technique and the full numerical model under two validation processes: (i) using different sets of input/output data; (ii) the application of the identified RNN-FAB model to HB analysis in lieu of the full numerical model of the FAB.

A spacecraft formation possesses several benefits over a single-satellite mission. However, launching a fleet of satellites is a high-cost, high-risk venture. One way to mitigate much of this risk is to demonstrate hardware and algorithm performance in groundbased testbeds. It is typically difficult to experimentally replicate satellite dynamics in an Earth-bound laboratory because of the influences of gravity and friction. An air bearing provides a very low-torque environment for experimentation, thereby recapturing the freedom of the space environment as effectively as possible. Depending upon con- figuration, air-bearing systems provide some combination of translational and rotational freedom; the three degrees of rotational freedom provided by a spherical air bearing are ideal for investigation of spacecraft attitude dynamics and control problems. An interest in experimental demonstration of formation flying led directly to the development of the Distributed Spacecraft Attitude Control System Simulator (DSACSS). The DSACSS is a unique facility, as it uses two air-bearing platforms working in concert. Thus DSACSS provides a pair of "spacecraft" three degrees of attitude freedom each. Through use of the DSACSS we are able to replicate the relative attitude dynamics between nodes of a formation such as might be required for co-observation of a terrestrial target. Many dissertations present a new mathematical technique or prove a new theory. This dissertation presents the design and development of a new experimental system. Although the DSACSS is not yet fully operational, a great deal of work has gone into its development thus far. This work has ranged from configuration design to nonlinear analysis to structural and electrical manufacturing. In this dissertation we focus on the development of the attitude determination subsystem. This work includes development of the equations of motion and analysis of the sensor suite dynamics. We develop nonlinear filtering techniques for data fusion and attitude estimation, and extend this problem to include estimation of the mass properties of the system. We include recommendations for system modifications and improvements. / Ph. D.

No description available.

Approved for public release; distribution in unlimited. / This thesis develops and implements a Control Moment Gyroscope (CMG) steering law, controller and active balancing system for a three-axis satellite simulator (TASS). The CMGs are configured in a typical pyramid configuration (the fourth CMG position being null). The development was done primarily with simulation and experiments utilizing Real Time Workshop and XPC Target of MATLAB and SIMULINK. The TASS is a double circular platform mounted on a spherical air bearing with the center of rotation (CR) about the approximate physical geometric center of the simulator. The TASS utilizes three moveable masses in the three body axes for balancing which actively eliminate any center of gravity (CG) offset and return the CG to the CR. The TASS supports an optics payload designed to acquire, track and point a received laser beam onto an off-satellite target. The target may be stationary or moving. Actively balancing the TASS reduces the torque output requirement for the CMGs while maintaining either a stabilized level platform or a particular commanded attitude. Reduction or elimination of torque output from the CMGs results in a more stabilized platform, less structural induced vibration, less jitter in payload optics and less power required in spacecraft applications. / Lieutenant Commander, United States Navy

Thesis (MEng) Stellenbosch University, 2014 / ENGLISH ABSTRACT: An Attitude Determination and Control System (ADCS) demonstrator and testing platform was required for satellite engineering students. The ADCS demonstrator and testing platform will allow students to develop insight into the concepts and challenges of ADCS design and implementation. The existing model nano-satellite EyasSAT was used as a design platform for a new ADCS demonstrator. A new ADCS module (ADCS_V2) was developed to replace the existing EyasSAT ADCS module. The new module allows for three-axis ADCS and the demonstration of the ADCS on an air bearing platform. The air bearing allows full freedom of movement for yaw rotations with limited pitch and roll rotations. The actuators and sensors required for the ADCS were developed and integrated into EyasSAT. In addition a new PCB was designed to form the ADCS_V2 module. Attitude determination algorithms and attitude control algorithms were implemented and tested using MATLAB Simulink simulations. These algorithms were then implemented on the ADCS_V2 module. The ADCS was tested using Hardware In the Loop (HIL) techniques and an air bearing. The yaw attitude of EyasSAT could be controlled within 0.4 degrees accuracy with all the sensors active. In order to stabilize the air bearing platform, the pitch and roll angles were rate controlled. The pitch and roll rates were damped to within 6 mrad/s. / AFRIKAANSE OPSOMMING: ’n Oriëntasiebepaling en Beheerstelsel (OBBS) demonstrasie en toets platform was benodig vir satellietingenieurswese studente. Die nuwe OBBS sal studente toelaat om insig te ontwikkel met betreking tot die idees en uitdagings wat verband hou met die ontwikkeling en implementering van ’n OBBS. Die huidige nano-sateliet model EyasSAT was gebruik as ’n ontwerpsbasis vir die nuwe OBBS. Die nuwe OBBS was ontwikkel om die huidige module van EyasSAT te vervang. Die nuwe OBBS laat oriëntasiebepaling en -beheer in drie asse toe. Die nuwe OBBS en EyasSAT kan die werking van ’n OBBS demonstreer op ’n luglaerplatform. Die luglaer laat vrye rotasie om die gierhoek toe terwyl die rol- en stygings-as beperk word. Die aktueerders en sensors wat benodig word vir die OBBS is ontwikkel en geïntegreer in EyasSAT saam met ’n nuwe gedrukte stroombaanbord om die nuwe OBBS te vorm. Orientasiebepaling en orientasiebeheer algoritmes is geïmplementeer en getoets met die hulp van MATLAB Simulink simulasies. Die algoritmes was op die OBBS module geïmplementeer en getoets deur gebruik te maak van HIL tegnieke en praktiese toetse op die luglaer. Die rotasie hoek van EyasSAT kan met ’n akkuraatheid van 0.4 grade beheer word indien al die sensors gebruik word. Die rol en stygingshoeksnelheid was gekanselleer om die luglaer stabiel te hou. Die hoeksnelheid van die twee asse kon tot kleiner as 6 mrad/s beheer word.

<p>  </p> <p>The development of the semiconductor industry is encountering a giant leap recently as Moorse’s is extended to the next levels. Advanced nanomanufacturing technology is the major challenge in the way. Higher resolution down to a few nanometers as well as higher throughput is always the key. As the optical lithography determines the feature size, the photomask is still in need of a low-cost and high resolution maskless patterning tool. In another aspect, the growing information allows the generation and storage of data at ever faster rates, which has led to the era of big data reaching a heroic amount of 7 zettabytes of total data in 2020. Future growth requires the total shipment of data storage capacity to double roughly every two years or less. For the future generation of magnetic data storage, the bit patterned medium (BPM) in combination with the current heat assisted magnetic recording (HAMR) is expected to increase the areal storage capacity by another order of magnitude by physically isolating magnetic bits at the nanoscale. Electron beam lithography (EBL) as a universal maskless lithography technique shows great resolution but has a high tool cost and low process throughput. Scanning probe lithography (SPL) is another family of nanoscale patterning techniques with low tool cost but the practical throughput is still limited. For example, dip pen nanolithography utilizes an AFM probe as a writing pen in direct patterning, but the ink delivery is limited by the rate of ink’s capillary transport. Other SPLs such as thermal probes with capabilities of 3D fabrication and surface oxidation via chemical reactions are all facing similar limitations in throughput. One way of breaking this limitation is to use parallel writing with millions of probes which also faces uniformity problems. </p> <p>In this Ph.D. dissertation, we report our Surfing Scanning Probe lithography (SSPL) method which can boost the scanning speed of SPL by several orders of magnitudes at a low cost by using a hydro-aero-dynamic scanning scheme. We use a homemade patterning head to continuously scan over a partially-wet spinning substrate at a linear speed of meters per second. The head carries several metallic tips which emit electrons and induce electrochemical reactions inside a gap of 10 nm scale. We use a liquid phase precursor and deliver it using the near-field electrospinning method and microfluid structures during the fast patterning. The best linewidth demonstrated is about 15 nm in full-width half maximum (FWHM) which can be further improved using smaller scanning gaps and sharp probe tips. Besides direct writing with a liquid precursor, SSPL can work with gas precursors as well enabled by nano plasma. The rate of material deposition is much high than conventional SPL. The SSPL system is a low-cost nanopatterning technology to produce patterns at high throughput and high resolution.</p>

Without lubrication, machines are not imaginable to perform over a long period of time and complete their designated operations. With its omnipresent availability, the air is capable of functioning as a lubricant in long operations very efficiently. Moreover, thrust bearings support axial loads and transmit power at the same time under heavy loads. Therefore, to provide separation under heavy loads in lubricated rotating devices such as thrust pad bearings keeping the power losses at a minimum, film thickness and pressure distribution are very important to investigate at the bearing interfaces. Thrust pad gas (air) bearings are being used in very high-speed rotating machines. Usages of these air bearings are increasing nowadays in industries. In this thesis project, simulations of lubricated contacts of a thrust pad air bearing are performed utilizing multiphysics phenomena and surface textures as mathematical functions. Structural mechanics and fluid mechanics physics are used to model multiphysics functionality. Ideal surface texture models defined by mathematical functions are utilized. More efficient techniques such as homogenization techniques to model the influences of surface roughness are introduced for multiscale study. The current work also presents the Reynolds equation for incompressible and iso-viscous Newtonian fluid flow and formulation for a stationary study. The air bearing with three pads is presented and a virtual twin of this model is built for simulation in COMSOL Multiphysics software. Simulation results are obtained using a single pad from the air bearing considering periodicity of the mathematical formulation. Numerical solutions for pressure build-up and film thickness distributions are achieved from a stationary study performed in COMSOL Multiphysics. MATLAB is used for rigid body solutions. Numerical verification is carried out between the rigid body solutions from MATLAB and fluid physics solutions from COMSOL Multiphysics only for the simulations with tilting pad configuration. Obtained rigid body solutions are also compared to the trends of thrust pad bearing design diagrams to verify the modelling approach and the results. A tilting pad lubricating configuration is used for the thrust pad bearing first. Then pocket geometries for optimization of the bearing pads are explored. For that purpose, separate digital models of the bearing pad are built in COMSOL and analysed for the best performances. Material properties of steel AISI 4340 and Polylactic Acid (PLA) material are used to model virtual bearing pads. To understand the performance of the bearing better, its performance parameters such as load carrying capacity (LCC), relative power loss, and coefficient of friction torque (COT) solutions from the simulations of lubricated contacts of the thrust pad air bearing are analysed. To characterize the performance of the bearing, dimensionless LCC, relative power loss, and COT are explicitly formulated and computed from the pressure and film thickness solutions obtained in the simulations. Relative power loss and COT are resulted from the development of shear stresses in the lubricating fluid due to motion. Parametric analysis is also performed for these parameters in COMSOL Multiphysics. Additionally, performances of several pocket geometry design configurations are also analysed for the best values reached such as the maximum LCC. Pockets with shallower depths are found to have provided higher LCC in general than deeper pocket geometries and plane pads with tilting pad lubricating configuration. Finally, a physical model of an air thrust pad bearing with 3D-printed bearing segments made of PLA material is tested. The physical bearing performed very well in achieving full film separation in the test.